Deco with too less air, options from the book

[Chatterton]

You are correct in that millions and millions of dives have been made on the USN tables. At the same time, that data is misleading. There is little research or data available on those dives. The dive stats you mention are not research dives made to the limits of the tables to test the validity of those tables and then give us a realistic DCS incidence rate, like the USN did. They were just dives made by divers who did or did not appropriately pad the tables. The development was still done with about 100 dives.

The USN Tables have shortcomings. First, they are entirley based on a 1 FPS ascent rate, which conventional wisdom tells us is not the best approach. The USN tables will not work with a slower ascent rate. Period. You cannot use the USN tables, and use safety stops, or modified rates of ascent. When the USN uses the USN tables they ascend at 1 FPS.

At the same time, the USN is transitioning from the USN Tables, to the VPM Tables. The reasoning for this is because although the USN tables have served us well, there are better options based on current knowledge and research.

Cheers

JC

The statement that the Navy tables are based on only 100 dives with a 5% hit rate is a bit misleading. Millions of dives have been made by the Navy on its tables and there is not a 5% hit rate. They are one of the most used and most documented set of tables out there.

According to Larry Taylor, Diving Safety Coordinator at the University of Michigan, ŵhe US Naval Safety Center report on diving illness and safety (as described in SPUMS, Sept 1997, p. 179) stated that for the period 1990-1995, there were 648,488 logged dives with 382 reported cases of decompression sickness. That is more like a 0.06% hit rate.

 

[Chatterton]

The more diving you do, the more efficient your body's inert gas loadiing and unloading becomes. When we are planning a deep dive, we will make sure to make some ramp up dives in the days prior. It is akin to aerobic conditioning. Hence the problem with divers on Day 1.

Cheers

JC

Since the overwhelming majority of dives occur in the 60-90 foot range, it is reasonable to find the majority of hits in that range, but it may not have as much to do with being loose with monitoring time, depth, and staying on tables as you might think. Whether you are using tables or a computer to guide your dive, a significant percentage of DCS hits (I have heard 50%) happen to divers who are within all limits.

There is more going on, frankly, than we understand. DAN has recently shown that that a huge percentage of hits happen on the first day of a trip, and the vast majority of those happen on the first dive of that first day. Why? No one seems to know.

 

[Chatterton]

Pete,

There is not a single certification agnecy in the world that will tell you that 1 FPS, or 60 FPM is an acceptable ascent rate, especially directly to the surface. There is not a computer on the market today that will not go totally crazy, and set off every alarm it has, if you ascend to the surface at that rate. Conventional wisdom, recent research, and hyperbaric scientists all agree that slower is better.

If you personally decide to ascend slower than 1 FPS, you are not following the USN Tables. If you makie up your own ascent rate, or incorporate safety stops, then you are not really using the table, are you? I do not know of anyone who actually uses the USN tables any more, and I would even hazard a guess that the divers expousing their use on this thread are not really following the tables as they are supposed to be used.

The USN tables did a great job getting us here. Now it is time to let them go, just like the USN is doing (for VPM), and just like we did with horsecollar BC's, two hose regulators, and black rubber mask skirts. Use any modern table, computer, or algorithm and debate the benefits or detriment of their use, but the USN tables are pretty much dive history.

You know that I still love you, man, and only want you to dive like it is 1999.


CHeers

JC

The thing is that computers and newer tables is that they tend to have more padding built into them. The old Navy tables not so much.

The Navy tables are very reliabal if you follow them exactly and are the most proven one ever used. In the 10 to 60 foot range no other tables have anywhere near the number of dives on them - why? - because that is the range for hull maintinance.

When you think about the number of dives that are done on ships hulls for inspcestion, cleaning, repair, and maintanince, no other table has the track record.

But these tables do not:

1 - Give you credit for multi-level diving
2- Will keep you in the water longer then some others because of #1
3 - Work on what some call a Bend Me/Fix Me process. You do the deco shallow where most modern theory has you doing it deeper to prevent micro bubbles

I don't dive Navy tables as a standard practice, but I have a copy on me for all deco dives. If things go real south - lost computer, lost buddy, lost anchor line, I still have a timer and depth gage and a set of tables.

Even for some mix dives they will work. As long as the O2 is 21%, (He% + N2%=79% with He less then 35%) and you have one deco gas, air tables will get you out of Hell.

 

[Chatterton]

I had to ask Howard if I was allowed to make 5 posts in a row? He told me I could, but I still feel a little crazy about it. Anyway, blame him.

I have always loved Run Time, and never use anything else when making a table!!! You can refer to the table at any time and always know where you are supposed to be. Some times it can be a little confusing trying to do math on the hang, especially with a lot of stops. The only thing I love more is a good dive computer that gives me a cieling instead of stops.

I will now be quiet. Thanks for your patience.


Cheers

JC

WAy off topic I know, but...

You don't use run time for deco dives?

 

[boulderjohn]

The only thing I love more is a good dive computer that gives me a cieling instead of stops.

JC

What a wonderful thing a reputation is!

If one of the "regular" thousands of SB members with a typical (lack of) reputation had written that sentence, there would be 5 pages of "You ignorant ****!" posts within 24 hours.

 

[scubadada]

Mr Chatterton,

What is the data to support the concept that nitrogen loading and unloading changes with the frequency of diving? This is not intuitively obvious to me and may run counter to physiologic principles.

Thanks, and good diving, Craig

The more diving you do, the more efficient your body's inert gas loadiing and unloading becomes. When we are planning a deep dive, we will make sure to make some ramp up dives in the days prior. It is akin to aerobic conditioning. Hence the problem with divers on Day 1.

Cheers

JC

 

[Chatterton]

Hey, I have to call em as I see em. Feel free to call me an Ignorant *****, as you wish. You will not be the first, or the last?

Actually, I am not even sure what I said that is "bad"? Is it using a computer, or using ceilings?

CHeers

JC

What a wonderful thing a reputation is!

If one of the "regular" thousands of SB members with a typical (lack of) reputation had written that sentence, there would be 5 pages of "You ignorant ****!" posts within 24 hours.

 

[boulderjohn]

Hey, I have to call em as I see em. Feel free to call me and Ignorant *****, as you wish. You will not be the first, or the last?

Actually, I am not even sure what I said that is "bad"? Is it using a computer, or using ceilings?

JC

That was not directed at you.

It was an observation of the atmosphere here on SB. Every time I have every seen anyone advocate computers for deco, it has sparked that negative reaction. The one exception is when I saw you make a similar observation in a past thread, and again there was no such response.

I myself do not have those feelings. I am only now taking advanced deco, but my tech instructor fairly spits when talking about computers, and you can be sure we will not be using them throughout any of my training.

 

[Chatterton]

Craig,

Unfortunatley, I am so not the scientific data guy. However, I am the empiracal knowledge guy. I am not sure exactly where I got it from to tell you the truth, but like I said, it seems to work for me on deep dives. Perhaps someone else has a source? Then again, maybe I am the only guy in the world to believe this?

How does this conflict with your view of human hyperbaric physiology?

Cheers

JC

Mr Chatterton,

What is the data to support the concept that nitrogen loading and unloading changes with the frequency of diving? This is not intuitively obvious to me and may run counter to physiologic principles.

Thanks, and good diving, Craig

 

[Gilldiver]

John, you may have missed this part:

<<I don't dive Navy tables as a standard practice, but I have a copy on me for all deco dives. If things go real south - lost computer, lost buddy, lost anchor line, I still have a timer and depth gage and a set of tables.>>


Like I said, I don't dive them but I do carry a set for the event I get handed a ticket to hell and need to get off that bus.

I will also use them as a touch stone to check a computer generated or Ratio Deco schedule. If they are less then Navy Tables or close to them, I will check very closly to find out where the error is. Because there is an error if a modern table is getting me near Navy stops.

I also wanted to point out to anyone that there is a range in the Navy table where you have to very carfull due to the required deco obligations.

Give me a call when you are passing through or have time to get wet up your way. I still have those videos from to English Channel to show you.